You want to keep it as is with the calci sand?
Tiny geckoes might be only option but I know you dont like geckoes.
If you remove the calci sand
dwarf hamsters you already have so thats out but a couple of firebelly toads might be something to consider if your child doesnt mind dropping crickets in there ,etc to feed them.
Even newts are good and no need to feed crickets.
If you want the calci sand look its limiting to tiny geckoes or small desert type snakes like shovelnose but those are all boring pets for a child.
Those African pygmy mice are interesting or zebra mice.